1. Technical Field
The invention generally relates to a movement device moving a movement body along one axis direction, and more particularly, to a movement device moving a movement body along one axis direction by a linear motor.
2. Description of Related Art
A movement device moving a movement body in one axis direction by a linear motor is well known in metal processing devices, transportation devices, inspection devices, measurement devices and semiconductor fabrication devices. Comparing the linear motor to a combination of a rotational motor and a ball screw, the linear motor is not influenced by, such as, unwanted back rush. Accordingly, the linear motor is effective on high speed movement and precise positioning.
If a thrust along the one axis direction acts on the movement body including a mover of the linear motor, a rotational torque acts on the movement body about an axis, in which the axis is perpendicular to a plane including the center of gravity and a path of movement of the mover, and passes through the center of gravity. With the unwanted rotational torque, attitude of the movement body that is moving may be deflected. Especially when the movement body has a large weight or a guide mechanism has a low rigidity, the guide mechanism may not adequately maintain the attitude of the movement body.
Prior art document 1 discloses a stage device, in which a pair of linear motors is horizontally arranged and a third linear motor is additionally arranged on a plane that has a height different from that of the pair of linear motors. Controlling the attitude of a movement body is possible by controlling the thrust generated from each of the linear motors. The additional linear motor for compensating an unwanted rotational torque may lead to a huge stage device.
Prior art document 2 discloses a stage device that comprises an X stage, a Y stage and a wafer stage. The Y stage is disposed on the X stage and is movable along an X direction by a pair of parallel linear motors. The wafer stage is disposed on the Y stage, and is movable along a Y direction by another pair of parallel linear motors. The thrust of each of the pair of parallel linear motors is determined based on a position of the center of gravity of the moving stage.